Stable Rate of Slip Along the Karakax Section of the Altyn Tagh Fault from Observation of Interglacial and Postglacial Offset Morphology and Surface Dating

Abstract

Digital elevation maps obtained using TanDEM‐X and Pleiades data combined with newly obtained surface age estimates using cosmogenic radionuclide (CRN) and optically simulated luminescence (OSL) methods are used to quantify the slip rate along the western section of the Altyn Tagh Fault in southern Xinjiang. The reconstruction of the conical shape of massive alluvial fans inferred to be from the Eemian (115±7 ka) from CRN dating shows consistent left‐lateral offsets of 300±20 m, yielding a slip rate of 2.6±0.3 mm/year. Successive episodes of incision have left cut terraces inset in wide canyons, 10–25 m below the fans' surface. The incision was followed by the deposition of a broad terrace of early Holocene age, which is reincised by modern stream channels. Near the village of Shanxili, a 200 m wide valley is partially dammed by a shutter ridge displaced by the fault. A fill terrace deposited upstream from the ridge has an OSL age of 8.8±0.6 ka. The 23±2 m offset of the riser incising the terrace indicates a minimum postdepositional movement on the fault, yielding a Holocene rate of 2.6±0.5 mm/year, consistent with the 115‐ka average slip rate. Scarp degradation analysis using mass diffusion reveals a nonlinear relationship between fault displacement and degradation coefficient along the progressively exposed fault scarp, a pattern suggesting either seismic clustering or variable diffusion rate since the Eemian. Together with the Gozha Co‐Longmu Co fault to the south, the Karakax section of the Altyn Tagh Fault contributes to the eastward movement of the western corner of Tibet.

Block Tectonics Across Western Tibet and Multi‐Millennial Recurrence of Great Earthquakes on the Karakax Fault

“…Lastly, it should be noted that the offset of the T3′/T3 riser at Taersa (∼255 ± 10 m) is commensurate with that of the corresponding Eemian T4 fan reconstruction (300 ± 20 m) at Site 4 in Peltzer et al. (2020) located 18 km to the east (Figure 1b).…”

“…This was also consistent with a convergence rate between India and Asia formerly estimated to be as large as ∼5 cm/yr based on Nuvel 1 and plate tectonic reconstructions (DeMets et al., 1990). Later on, quantitative field measurements and sampling suggested a slip rate bracket of 12–25 mm/yr in the last ∼115 ka (Ryerson et al., 1999; dataset published in Peltzer et al., 2020). Much slower slip rates, however, have been proposed in recent years.…”

Late Pleistocene slip rate of the central Haiyuan fault constrained from optically stimulated luminescence, 14C, and cosmogenic isotope dating and high-resolution topography

“…Finally, to avoid the ambiguity in correlating terrace surface ages with their upper or lower risers, the offset of the terrace itself may be determined (e.g., Lensen, 1964;Peltzer et al, 1988Peltzer et al, , 2020. In general, this is possible when the terraces bear particular syndepositional geomorphic markers at their surface (channels, ridges) or if the terraces have specific inherited shapes (fan shapes, slopes) that enables unambiguous geometric reconstructions.…”

STEPS: Slip Time Earthquake Path Simulations Applied to the San Andreas and Toe Jam Hill Faults to Redefine Geologic Slip Rate Uncertainty

“…A geologic deformation model may be produced in conjunction with geodetic deformation models, which are based primarily on GPS data. In the Uniform California Earthquake Rupture Forecast, version 3 (UCERF3), four deformation models were implemented with varying usage of geologic input data (Parsons et al, 2013), which incorporated per-earthquake uncertainty of long-term geologic slip rates. Additionally, two geodetic-based deformation models were implemented across the western U.S. in the U.S. National Seismic Hazard Model (NSHM) of 2014 (Petersen et al, 2015).…”

“…Due to the time scales over which they average, geologic slip rates necessarily integrate multiple earthquake cycles into a single rate value. Geologic slip rates have been interpreted as constant over millennial time scales (e.g., Chevalier et al, 2012;Gold & Cowgill, 2011;Hubert-Ferrari et al, 2002;Noriega et al, 2006;Peltzer et al, 2020;Salisbury et al, 2018;Weldon & Sieh, 1985) but have also been shown to vary over centennial to millennial time scales across faults of various kinematics and strain rates (e.g., Burgette et al, 2020;Dolan et al, 2007;Friedrich et al, 2003;Gold & Cowgill, 2011;Gold et al, 2017;Hatem et al, 2020;Khajavi et al, 2018;Ninis et al, 2013;Onderdonk et al, 2015;Sharp, 1981;Wallace, 1987;Weldon et al, 2004;Zinke et al, 2017Zinke et al, , 2019. While observations of temporally variable geologic slip rates provide additional nuance into fault behavior from a tectonics standpoint (e.g., long-term record of earthquake clusters and lulls), their implementation in seismic hazard modeling remains challenging.…”